Linksys RTP300 User Guide - Page 23

Introducing Linksys Analog Telephone Adapters ATA Software Features SIP Proxy Redundancy In typical commercial IP Telephony deployments, all calls are established through a SIP proxy server. An average SIP proxy server may handle thousands of subscribers. It is important that a backup server be available so that an active server can be temporarily switched out for maintenance. The Linksys ATA device supports the use of backup SIP proxy servers (via DNS SRV) so that service disruption should be nearly eliminated. A relatively simple way to support proxy redundancy is to configure your DNS server with a list of SIP proxy addresses. The Linksys ATA device can be instructed to contact a SIP proxy server in a domain named in the SIP message. The Linksys ATA device consults the DNS server to get a list of hosts in the given domain that provides SIP services. If an entry exists, the DNS server returns an SRV record that contains a list of SIP proxy servers for the domain, with their host names, priority, listening ports, and so on. The Linksys ATA device tries to contact the list of hosts in the order of their stated priority. If the Linksys ATA device is currently using a lower priority proxy server, it periodically probes the higher priority proxy to see whether it is back on line, and switches back to the higher priority proxy when possible. SIP Proxy Redundancy is configured in the Line and PSTN Line tabs in the Administration Web Server. See "Linksys ATA Routing Field Reference," on page 86. Other Linksys ATA Software Features The following table summarizes other features provided by Linksys ATA devices. Feature Description Streaming Audio Server See "Configuring a Streaming Audio Server," on page 71. T.38 Fax Relay See "Using a FAX Machine (SPA2102, SPA3102 or SPA8000)," on page 45. Silence Suppression See "Silence Suppression and Comfort Noise Generation," on page 48. Modem and Fax PassThrough • Modem pass-through mode can be triggered only by predialing the number set in the Modem Line Toggle Code. (Set in the Regional tab.) • FAX pass-through mode is triggered by a CED/CNG tone or an NSE event. • Echo canceller is automatically disabled for Modem pass-through mode. • Echo canceller is disabled for FAX pass-through if the parameter FAX Disable ECAN (Line 1 or 2 tab) is set to "yes" for that line (in that case FAX pass-through is the same as Modem pass-through). • Call waiting and silence suppression is automatically disabled for both FAX and Modem pass-through. In addition, out-of-band DTMF Tx is disabled during modem or fax pass-through. Adaptive Jitter Buffer The Linksys ATA device can buffer incoming voice packets to minimize outof-order packet arrival. This process is known as jitter buffering. The jitter buffer size proactively adjusts or adapts in size, depending on changing network conditions. The Linksys ATA device has a Network Jitter Level control setting for each line of service. The jitter level determines how aggressively the Linksys ATA device tries to shrink the jitter buffer over time to achieve a lower overall delay. If the jitter level is higher, it shrinks more gradually. If jitter level is lower, it shrinks more quickly. Adaptive Jitter Buffer is configured in the Line and PSTN Line tabs. See "Linksys ATA Voice Field Reference," on page 94. Linksys ATA Administration Guide 23